The purpose of this letter is to bring to your attention an error in a sample size formula appearing in a 2005 article published in this journal. The article described the development of a head and face anthropometric survey of U.S. respirator users. The sample size formula (n = (1.96× CV/a)2× 1.534) that was used in the development of that survey and subsequently reported in the article was incorrect. The authors of that article intended to use the sample size formula published in the ISO 15535 standard "General Requirements for Establishing an Anthropometric Database" (n = (1.96 × CV/a)2× 1.5342). Since there was an error in the sample size calculation (missing ^2), an analysis was conducted and described to understand the possible implications of the error.